Recent advances in Internet technology have changed the way we exchange information. Ubiquitous use of the Internet has led to the idea of convergence, The different types of data (e.g. video, sounds, pictures and text) must traverse the same network, and this has given rise to a plethora of protocols which aim to transmit real time and data traffic on a single network with quality of service support.
Chief among these protocols are DiffServ, IntServ and MPLS, which each require packet classification (i.e. determination of the packet's type) in real time when it is received. The first step in this classification is to extract relevant bytes from a packet, “parsing”. This is described in Chapter I of “Computer Networks”, Andrew S Tanenbaum, Prentice Hall 2nd Ed, 1988.
The parsing operation includes determining whether the packet includes tags. For example, conventionally Ethernet packets may include a VLAN (virtual local area network) tag—i.e. a tag which indicates a VLAN associated with the packet. A VLAN tag is conventionally 4-bytes inserted into the Ethernet frame between the Source MAC Address field and the Length/Type field. The first 2 bytes of the VLAN tag are always set to a value of 0x8100, while the second two bytes are control information (user priority field, canonical format indicator and VLAN identifier).
Another type of tag is defined by the SNAP protocol (subnetwork access protocol), which was introduced to allow older frames and protocols to be encapsulated in a Type 1 LLC header so making any protocol ‘pseudo-IEEE compliant’. The SNAP tag (or “snap encapsulation”) is placed directly after the standard length/type field of the Ethernet packet (which always takes a value less than or equal to 1500), and has AA-AA as its first two bytes. A packet containing a SNAP tag is called SNAPped.
Generally, an Ethernet packet is made up of levels of nested data, known as layers. Data which is interpreted directly by a machine is called “layer 1”, or physical layer, data. “Layer 2”, or data link layer, data is LAN (local area network) data, such as MAC (media access control) data uniquely identifying an adapter on the LAN. Within the “layer 2” packet may be “layer 3”, or network layer, data defining among other things the IP source address and destination address of the packet. Within the layer 3 packet may be “layer 4” data, or transport layer data, e.g. TCP (transmission control protocol) data.
In view of the great variety of protocols which may be encountered, it would be useful to provide a parsing technique which is highly flexible.
Additionally, there are a variety of circumstances in which it would be useful to parse a plurality of concurrently received data packets. Such circumstances are not limited to Ethernet applications, but, taking Ethernet applications as an example, in a co-pending pending application referred to above, the present inventors propose a configurable Ethernet switch which can function both as a Fast Ethernet and as a Gigabit Ethernet switch, in order to facilitate the transition from FE to GE Ethernet. A data port can be operated as eight FE MAC interfaces or alternatively as a single GE MAC interface. In the former case, it may happen that the eight FE interfaces receive packets at the same time. It would be possible-to provide sufficiently large buffers at the input port that all of these packets are completely received before the processing of any one of the packets begins, but this increases the cost of the buffers required. It would instead be useful to be able to process all of the packets concurrently (“on-the-fly”) as they are received to reduce the buffering requirement.